The stress response of three-spined sticklebacks is modified in proportion to effluent exposure downstream of wastewater treatment works

Review of ecologically relevant in vitro bioassays to supplement current in vivo tests for whole effluent toxicity testing - Part 2: Non-apical endpoints

Whole effluent toxicity (WET) testing uses whole animal exposures to assess the toxicity of complex mixtures, like wastewater. These assessments typically include four apical endpoints: mortality, growth, development, and reproduction. In the last decade, there has been a shift to alternative methods that align with the 3Rs to replace, reduce, and refine the use of animals in research. In vitro bioassays can provide a cost-effective, high-throughput, ethical alternative to in vivo assays. In addition, they can potentially include additional, more sensitive, environmentally relevant endpoints than traditional toxicity tests. However, the ecological relevance of these endpoints must be established before they are adopted into regulatory frameworks. This is Part 2 of a two-part review that aims to identify in vitro bioassays that are linked to ecologically relevant endpoints that could be included in WET testing. Part 2 of this review focuses on non-apical endpoints that should be incorporated into WET testing. In addition to the four apical endpoints addressed in Part 1, this review identified seven additional toxic outcomes: endocrine disruption, xenobiotic metabolism, carcinogenicity, oxidative stress, inflammation, immunotoxicity and neurotoxicity. For each, the response at the molecular or cellular level measured in vitro was linked to the response at the organism level through a toxicity pathway. Literature from 2015 to 2020 was used to identify suitable bioassays that could be incorporated into WET testing.

Wild longnose dace downstream of wastewater treatment plants display an obese phenotype

Wild fish living downstream of wastewater treatment plants (WWTPs) often have increased body condition factors or body mass indices compared to upstream fish. This observation has been largely attributed to increased nutrient loading and food availability around wastewater effluent outflows. While a higher condition factor in fish is generally considered a predictor of healthy ecosystems, the metabolic status and capacity of the animals downstream of WWTPs may be a better predictor of fitness and potential population level effects. To address this, we sampled wild longnose dace (Rhinichthys cataractae), a native species in North American waterways, from sites upstream and downstream of WWTPs. Downstream fish had higher body mass indices, which corresponded with higher nutrient (lipid, protein, and glycogen) storage in somatic tissues compared to upstream fish. Liver transcriptome analysis revealed metabolic reprogramming favoring lipid synthesis, including higher hepatic triglyceride levels and transcript abundance of targeted lipogenic genes. This suggests that effluent exposure-mediated obesity in dace is a result of changes at the transcriptional level. To determine potential ecological consequences, we subjected these fish to an acute stressor in situ to determine their stress performance. Downstream fish failed to mobilize metabolites post-stress, and showed a reduction in liver aerobic and anaerobic metabolic capacity. Taken together, fish living downstream of WWTPs exhibit a greater lipid accumulation that results in metabolic disruption and may compromise the ability of these fish to cope with subsequent environmental and/or anthropogenic stressors.

Hormonal and behavioural effects of motorboat noise on wild coral reef fish

Anthropogenic noise is an emergent ecological pollutant in both terrestrial and aquatic habitats. Human population growth, urbanisation, resource extraction, transport and motorised recreation lead to elevated noise that affects animal behaviour and physiology, impacting individual fitness. Currently, we have a poor mechanistic understanding of the effects of anthropogenic noise, but a likely candidate is the neuroendocrine system that integrates information about environmental stressors to produce regulatory hormones; glucocorticoids (GCs) and androgens enable rapid individual phenotypic adjustments that can increase survival. Here, we carried out two field-based experiments to investigate the effects of short-term (30 min) and longer-term (48 h) motorboat-noise playback on the behaviour, GCs (cortisol) and androgens of site-attached free-living orange-fin anemonefish (Amphiprion chrysopterus). In the short-term, anemonefish exposed to motorboat-noise playback showed both behavioural and hormonal responses: hiding and aggression increased, and distance moved out of the anemone decreased in both sexes; there were no effects on cortisol levels, but male androgen levels (11-ketotestosterone and testosterone) increased. Some behaviours showed carry-over effects from motorboat noise after it had ceased, and there was no evidence for a short-term change in response to subsequent motorboat-noise playback. Similarly, there was no evidence that longer-term exposure led to changes in response: motorboat noise had an equivalent effect on anemonefish behaviour and hormones after 48 h as on first exposure. Longer-term noise exposure led to higher levels of cortisol in both sexes and higher testosterone levels in males, and stress-responses to an additional environmental challenge in both sexes were impaired. Circulating androgen levels correlated with aggression, while cortisol levels correlated with hiding, demonstrating in a wild population that androgen/glucocorticoid pathways are plausible proximate mechanisms driving behavioural responses to anthropogenic noise. Combining functional and mechanistic studies are crucial for a full understanding of this global pollutant.

Towards Non-Invasive Methods in Measuring Fish Welfare: The Measurement of Cortisol Concentrations in Fish Skin Mucus as a Biomarker of Habitat Quality

Cortisol levels in fish skin mucus have shown to be good stress indicators in farm fish exposed to different stressors. Its applicability in free-ranging animals subject to long-term environmental stressors though remains to be explored. The present study was therefore designed to examine whether skin mucus cortisol levels from a wild freshwater fish (Catalan chub, Squalius laietanus) are affected by the habitat quality. Several well-established hematological parameters and cortisol concentrations were measured in blood and compared to variations in skin mucus cortisol values across three habitats with different pollution gradient. Fluctuations of cortisol in skin mucus varied across the streams of differing habitat quality, following a similar pattern of response to that detected by the assessment of cortisol levels in blood and the hematological parameters. Furthermore, there was a close relationship between cortisol concentrations in skin mucus and several of the erythrocytic alterations and the relative proportion of neutrophils to lymphocytes. Taken together, results of this study provide the first evidence that skin mucus cortisol levels could be influenced by habitat quality. Although results should be interpreted with caution, because a small sample size was collected in one studied habitat, the measurement of cortisol in skin mucus could be potentially used as a biomarker in freshwater fish.

Municipal wastewater effluent affects fish communities: A multi-year study involving two wastewater treatment plants

Although effluent from municipal wastewater treatment plants (WWTPs) is a major stressor in receiving environments, relatively few studies have addressed how its discharge affects natural fish communities. Here, we assessed fish community composition over three years along a gradient of effluent exposure from two distinct WWTPs within an International Joint Commission Area of Concern on the Great Lakes (Hamilton Harbour, Canada). We found that fish communities changed with distance from both WWTPs, and were highly dissimilar between sites that were closest to and furthest from the wastewater outfall. Despite differences in the size and treatment technology of the WWTPs and receiving habitats downstream, we found that the sites nearest the outfalls had the highest fish abundances and contained a common set of signature fish species (i.e., round goby Neogobius melanostomus, green sunfish Lepomis cyanellus). Non-native and stress tolerant species were also more abundant near one of the studied WWTPs when compared to the reference site, and the number of young-of-the-year fish collected did not vary along the effluent exposure gradients. Overall, we show that fish are attracted to wastewater outfalls raising the possibility that these sites may act as an ecological trap.

What Works? the Influence of Changing Wastewater Treatment Type, Including Tertiary Granular Activated Charcoal, on Downstream Macroinvertebrate Biodiversity Over Time

The present study reviewed the impacts of wastewater on macroinvertebrates over 4 decades in a United Kingdom lowland river. This involved examining changes in chemicals, temperature, flow, and macroinvertebrate diversity from the 1970s until 2017 for a wastewater-dominated river downstream of Swindon in the United Kingdom (population ~ 220 000). When the wastewater treatment process changed from trickling filter to activated sludge in 1991, biological oxygen demand was nearly halved (90th percentile from 8.1 to 4.6 mg/L), ammonia peaks dropped more than 7-fold (90th percentile from 3.9 to 0.53 mg/L), whereas dissolved oxygen climbed consistently above 60% saturation (10th percentile from 49 to 64%) at a sampling point 2 km downstream of the wastewater treatment plant. A sustained increase in the number of macroinvertebrate species was evident from that point. River flow did not change, temperature rose slightly, and the major metal concentrations declined steadily over most of the monitoring period. Neither the introduction of phosphate stripping in 1999 nor the use of tertiary granular activated charcoal from 2008 to 2014 had strong positive effects on subsequent macroinvertebrate diversity. That the diversity still had not reached the ideal status by 2016 may be related to the modest habitat quality, agricultural pesticides, and limited recolonization potential in the catchment. The results indicate that urban wastewaters, with their chemical pollutants, are today probably not the biggest threat to the macroinvertebrate diversity of multiply stressed lowland rivers in the United Kingdom. Environ Toxicol Chem 2019;38:1820-1832. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Variation in scale cortisol concentrations of a wild freshwater fish: Habitat quality or seasonal influences?

A significant body of literature suggests that aquatic pollutants can interfere with the physiological function of the fish hypothalamic-pituitary-interrenal (HPI) axis, and eventually impair the ability to cope with subsequent stressors. For this reason, development of accurate techniques to assess fish stress responses have become of growing interest. Fish scales have been recently recognized as a biomaterial that accumulates cortisol, hence it can be potentially used to assess chronic stress in laboratory conditions. We, therefore, aimed to evaluate the applicability of this novel method for cortisol assessment in fish within their natural environment. Catalan chub (Squalius laietanus) were sampled from two sites; a highly polluted and a less polluted (reference) site, in order to examine if habitat quality could potentially influence the cortisol deposition in scales. We also evaluated the seasonal variation in scale cortisol levels by sampling fish at three different time points during spring-summer 2014. In each sampling, blood was collected to complement the information provided by the scales. Our results demonstrated that blood and scale cortisol levels from individuals inhabiting the reference site were significantly correlated, therefore increasing the applicability of the method as a sensitive-individual measure of fish HPI axis activity, at least in non-polluted habitats. Since different environmental conditions could potentially alter the usefulness of the technique, results highlight that further validation is required to better interpret hormone fluctuations in fish scales. Scale cortisol concentrations were unaffected by habitat quality although fish from the polluted environment presented lower circulating cortisol levels. We detected a seasonal increase in scale cortisol values concurring with an energetically costly period for the species, supporting the idea that the analysis of cortisol in scales reveals changes in the HPI axis activity. Taken together, the present study suggests that cortisol levels in scales are more likely to be influenced by mid-term, intense energetically demanding periods rather than by long-term stressors. Measurement of cortisol in fish scales can open the possibility to study novel spatio-temporal contexts of interest, yet further research is required to better understand its biological relevance.

Altered non-reproductive behavior and feminization caused by developmental exposure to 17α-ethinylestradiol persist to adulthood in three-spined stickleback (Gasterosteus aculeatus)

The synthetic estrogen 17α-ethinylestradiol (EE₂), ubiquitous in the aquatic environment and commonly detected in sewage effluents, interferes with the endocrine system in multiple ways. Exposure during sensitive windows of development causes persistent effects on fertility, reproductive and non-reproductive behavior in mammals and fish. In the present study, three-spined stickleback (Gasterosteus aculeatus) were exposed to nominal 0 and 20 ng/L EE₂ from fertilization to 7 weeks post-hatch. After 8 months of remediation in clean water three non-reproductive behaviors, not previously analyzed in developmentally EE₂-exposed progeny of wild-caught fish, were evaluated. Chemical analysis revealed that the nominal 0 and 20 ng/L exposure contained 5 and 30 ng/L EE_2, respectively. Therefore, the use of control fish from previous experiments was necessary for comparisons. Fish exposed during development showed significant concentration-dependent reduction in anxiety-like behavior in the scototaxis (light/dark preference) test by means of shorter latency to first entrance to the white compartment, more visits in white, and longer total time in white compared to unexposed fish. In the novel tank test, developmental exposure significantly increased the number of transitions to the upper half of the aquaria. Exposure to EE₂ during development did not alter shoal cohesion in the shoaling test compared with unexposed fish but fish exposed to 30 ng/L EE₂ had significantly longer latency to leave the shoal and fewer transitions away from the shoal compared to fish exposed to 5 ng/L EE₂. Skewed sex ratio with more females, sex reversal in genetic males as well as intersex in males was observed after exposure to 30, but not 5 ng/L EE₂. In conclusion, EE₂ exposure during development in three-spined stickleback resulted in persistent effects on anxiety-like behaviors. These long-term effects from developmental exposure are likely to be of higher relevance for natural populations than are short-term effects from adult exposure.

Acute stress response of fathead minnows caged downstream of municipal wastewater treatment plants in the Bow River, Calgary

We examined whether exposure to municipal wastewater effluent (MWWE) compromised the stress performance of laboratory-reared fathead minnows (Pimephales promelas) in a field setting. Adult minnows were caged at two sites upstream and three sites downstream of wastewater treatments plants (WWTPs) discharging MWWE into the Bow River, Calgary, Alberta, Canada. At each site one group of fish was sampled after a 26 day exposure to MWWE, while another group was subjected to 1-min air exposure followed by 60-min confinement and then sampled. Fish morphometrics and proximate composition were measured, and whole-body cortisol, glucose and lactate levels assessed as markers of the stress response. The whole-body protein, glycogen and lipid content were higher at the site closest to a WWTP outfall relative to the other downstream and upstream sites. There were no significant differences in whole-body cortisol levels in minnows sampled at sites either upstream or downstream of WWTPs. Acute stressor exposure significantly elevated whole-body cortisol levels in all groups, and this response was not modified by the location of the sampling sites. The whole-body metabolite profile, including glucose and lactate levels, were significantly higher in fish caged immediately downstream from WWTP inputs relative to upstream sites. There was an acute-stressor-mediated increase in whole-body lactate, but not glucose, levels and this response was independent of sampling site. The results reveal that the capacity to evoke an acute stress response was not compromised in fathead minnows caged for 26 days downstream of WWTPs in the Bow River. However, there were changes in the whole-body proximate composition and metabolite levels immediately downstream from the WWTP outfall suggesting greater accumulation of energy stores in these fish. Taken together, our results suggest that environmental factors in addition to contaminants, including higher water temperature and nutrient availability, influence the impact of MWWEs on fish stress performance.

Risky business: Changes in boldness behavior in male Siamese fighting fish, Betta splendens, following exposure to an antiandrogen

Components of boldness, such as activity level and locomotion, influence an individual's ability to avoid predators and acquire resources, generating fitness consequences. The presence of endocrine disrupting chemicals (EDCs) in the aquatic environment may affect fitness by changing morphology or altering behaviors like courtship and exploration. Most research on EDC-generated behavioral effects has focused on estrogen mimics and reproductive endpoints. Far fewer studies have examined the effects of other types of EDCs or measured non-reproductive behaviors. EDCs with antiandrogenic properties are present in waterways yet we know little about their effects on exposed individuals although they may produce effects similar to those caused by estrogen mimics because they act on the same hormonal pathway. To examine the effects of antiandrogens on boldness, this study exposed male Siamese fighting fish, Betta splendens, to a high or low dose of one of two antiandrogens, vinclozolin or flutamide, and observed behavior in three boldness assays, both before and after exposure. Overall, antiandrogen exposure increased boldness behavior, especially following exposure to the higher dose. Whether or not antiandrogen exposure influenced boldness, as well as the nature and intensity of the effect, was assay-dependent. This demonstrates the importance of studying EDC effects in a range of contexts and, at least within this species, suggests that antiandrogenic compounds may generate distinct physiological effects in different situations. How and why the behavioral effects differ from those caused by exposure to an estrogen mimic, as well as the potential consequences of increased activity levels, are discussed. Exposure to an antiandrogen, regardless of dose, produced elevated activity levels and altered shoaling and exploration in male Siamese fighting fish. These modifications may have fitness consequences.

Modulation of the stress response in wild fish is associated with variation in dissolved nitrate and nitrite

Disruption of non-reproductive endocrine systems in wildlife by chemicals has received little attention but represents a potentially significant problem. Nitrate is a major anthropogenic contaminant in the freshwater aquatic environment and has been identified as a potential disrupter of endocrine function in aquatic animals. This study was conducted to investigate the relationship between the function of the neuroendocrine stress axis in fish and inorganic N loading along reaches of rivers receiving cumulative point source and diffuse chemical inputs. To accomplish this, the responsiveness of the stress axis, quantified as the rate of release of cortisol to water across the gills during exposure to a standardised stressor, was measured in three-spined sticklebacks (Gasterosteus aculeatus L.) resident at three sites on each of four rivers in north-west England. The magnitude of the stress response in fish captured at the sites furthest downstream on all rivers was more than twice that of fish captured at upstream sites. Site-specific variation in stress axis reactivity was better explained by between-site variation in concentrations of dissolved nitrate, nitrite, and ammonia than by the concentration of wastewater treatment works effluent. An increase in the magnitude of the stress response was seen among sticklebacks at sites where long-term averaged concentrations of NH₃-N, NO₃-N and NO₂-N exceeded 0.6, 4.0 and 0.1 mg/L respectively. These data suggest that either (i) inorganic N is a better surrogate than wastewater effluent concentration for an unknown factor or factors affecting stress axis function in fish, or (ii) dissolved inorganic N directly exerts a disruptive influence on the function of the neuroendocrine stress axis in fish, supporting concerns that nitrate is an endocrine-modulating chemical.

Patterns of stress responses shift during seasonal life-history transitions: An analysis comparing baseline, maximal and integrated corticosterone in female red-sided garter snakes (Thamnophis sirtalis parietalis)

Glucocorticoids often rise and fall with a variety of external and internal cues and frequently vary among life-history stages. This suggests that changing glucocorticoids may coordinate life-history transitions. To explore this hypothesis, we asked if the time-course of stress-induced glucocorticoid levels differ between two life-history transitions (i.e., spring and fall migration) in female red-sided garter snakes (Thamnophis sirtalis parietalis). We collected non-migratory females from a communal den and migratory females from a road along the migration route and treated them with 4h of capture stress; plasma corticosterone was measured before, during and after capture stress. During the spring, den-collected females exhibited a stress-induced peak in corticosterone at an earlier sampling time than migrating, road-collected females. Because the pattern of corticosterone responses varied with migratory state, negative feedback on and/or sensitivity of the hypothalamus-pituitaryadrenal (HPA) axis may be linked to spring migration. During the fall, capture stress elicited an increase in corticosterone in den-collected females but not in migrating, road-collected females. Baseline corticosterone was higher and both maximal and integrated corticosterone responses were lower during the fall compared to spring, indicating that stress responses are smaller when baseline corticosterone is elevated, perhaps due to a "ceiling effect". These data suggest that HPA axis regulation changes during seasonal migration, possibly via altering negative feedback, HPA axis sensitivity, or some other mechanism. This study supports the hypothesis that glucocorticoids coordinate life-history events and suggests that examining a suite of stress response characteristics is most informative for understanding the function of HPA modulation.

Respirometry increases cortisol levels in rainbow trout Oncorhynchus mykiss: implications for measurements of metabolic rate

This study aimed to assess the extent to which chasing, handling and confining Oncorhynchus mykiss to a small respirometer chamber during respirometric experiments is stressful and affects metabolic measurements. The study observed increased cortisol levels in animals tested using a chase protocol and subsequent intermittent-flow respirometry, suggesting that this procedural treatment may stress animals.

Large microplastic particles in sediments of tributaries of the River Thames, UK - Abundance, sources and methods for effective quantification

Sewage effluent input and population were chosen as predictors of microplastic presence in sediments at four sites in the River Thames basin (UK). Large microplastic particles (1mm-4mm) were extracted using a stepwise approach to include visual extraction, flotation and identification using Raman spectroscopy. Microplastics were found at all four sites. One site had significantly higher numbers of microplastics than other sites, average 66 particles 100g^-1, 91% of which were fragments. This site was downstream of a storm drain outfall receiving urban runoff; many of the fragments at this site were determined to be derived of thermoplastic road-surface marking paints. At the remaining three sites, fibres were the dominant particle type. The most common polymers identified included polypropylene, polyester and polyarylsulphone. This study describes two major new findings: presence of microplastic particles in a UK freshwater system and identification of road marking paints as a source of microplastics.

CAPSULE

This study is the first to quantify microplastics of any size in river sediments in the UK and links their presence to terrestrial sources including sewage and road marking paints.

Long-term water quality data explain interpopulation variation in responsiveness to stress in sticklebacks at both wastewater effluent-contaminated and uncontaminated sites

The magnitude of the corticosteroid response to a standardized stressor varied in proportion to the concentration of effluent in three-spined sticklebacks (Gasterosteus aculeatus L.) captured downstream of 10 wastewater-treatment plants (WWTPs). However, at 9 sites with no upstream WWTP input interpopulation variation in the reactivity of the stress axis occurred across a similar range to that seen for fish at impacted sites, suggesting that the factor(s) responsible for modulating stress responsiveness in sticklebacks is not unique to sites receiving WWTP effluent. Physicochemical data from a long-term monitoring program were employed to investigate whether variation in water quality contributed to between-site variation in stress axis reactivity. Between-site variation in 14 water quality determinands explained between 30% and 60% of the variation in stress reactivity and fish size for sticklebacks at both WWTP-contaminated and uncontaminated sites. At uncontaminated sites the mean mass and length of sticklebacks increased with total oxidized nitrogen (N) concentration (as an indicator of anthropogenic input), whereas at WWTP-contaminated sites fish size decreased with increasing effluent concentration, suggesting that factors adversely affecting growth were present predominantly at WWTP-contaminated sites. In contrast, at both contaminated and uncontaminated sites the magnitude of the corticosteroid response to a standardized stressor increased with anthropogenic input (effluent concentration or total oxidized N, respectively), indicating that a factor or factors modulating the reactivity of the stress axis may be present at both WWTP-contaminated and uncontaminated sites. Environ Toxicol Chem 2016;35:3014-3022. © 2016 SETAC.

Home alone-The effects of isolation on uptake of a pharmaceutical contaminant in a social fish

A wide range of biologically active pharmaceutical residues is present in aquatic systems worldwide. As uptake potential and the risk of effects in aquatic wildlife are directly coupled, the aim of this study was to investigate the relationships between stress by isolation, uptake and effects of the psychiatric pharmaceutical oxazepam in fish. To do this, we measured cortisol levels, behavioral stress responses, and oxazepam uptake under different stress and social conditions, in juvenile perch (Perca fluviatilis) that were either exposed (1.03μgl^-1) or not exposed to oxazepam. We found single exposed individuals to take up more oxazepam than individuals exposed in groups, likely as a result of stress caused by isolation. Furthermore, the bioconcentration factor (BCF) was significantly negatively correlated with fish weight in both social treatments. We found no effect of oxazepam exposure on body cortisol concentration or behavioral stress response. Most laboratory experiments, including standardized bioconcentration assays, are designed to minimize stress for the test organisms, however wild animals experience stress naturally. Hence, differences in stress levels between laboratory and natural environments can be one of the reasons why predictions from artificial laboratory experiments largely underestimate uptake of oxazepam, and other pharmaceuticals, in the wild.

Selective estrogen receptor modulators differentially alter the immune response of gilthead seabream juveniles

17α-ethynylestradiol (EE2), a synthetic estrogen used in oral contraceptives and hormone replacement therapy, tamoxifen (Tmx), a selective estrogen-receptor modulator used in hormone replacement therapy, and G1, a G protein-coupled estrogen receptor (GPER) selective agonist, differentially increased the hepatic vitellogenin (vtg) gene expression and altered the immune response in adult gilthead seabream (Sparus aurata L.) males. However, no information exists on the effects of these compounds on the immune response of juveniles. This study aims, for the first time, to investigate the effects of the dietary intake of EE2, Tmx or G1 on the immune response of gilthead seabream juveniles and the capacity of the immune system of the specimens to recover its functionality after ceasing exposures (recovery period). The specimens were immunized with hemocyanin in the presence of aluminium adjuvant 1 (group A) or 120 (group B) days after the treatments ceased (dpt). The results indicate that EE2 and Tmx, but not G1, differentially promoted a transient alteration in hepatic vtg gene expression. Although all three compounds did not affect the production of reactive oxygen intermediates, they inhibited the induction of interleukin-1β (il1b) gene expression after priming. Interestingly, although Tmx increased the percentage of IgM-positive cells in both head kidney and spleen during the recovery period, the antibody response of vaccinated fish varied depending on the compound used and when the immunization was administered. Taken together, our results suggest that these compounds differentially alter the capacity of fish to respond to infection during ontogeny and, more interestingly, that the adaptive immune response remained altered to an extent that depends on the compound.

A comparison of two methods for the assessment of stress axis activity in wild fish in relation to wastewater effluent exposure

Riverine fish are particularly vulnerable to chemical exposure - rivers receive chemicals of anthropogenic origin from a variety of sources, one of the most significant being the chemically complex effluents discharged by wastewater treatment works (WWTWs). The extent to which non-reproductive components of the endocrine system in fish may be vulnerable to interference by contaminants associated with WWTW effluent is not well understood, but a significant body of evidence does suggest that contaminants present in the aquatic environment may interfere with the normal function of the neuroendocrine stress axis in fish. Field investigations of stress axis function in free-living populations of fish by measurement of hormone concentrations in blood can be confounded by the remoteness of sampling locations and the size of target species. Two methods for assessing stress axis reactivity in situations where blood samples are unavailable were compared in three-spined sticklebacks in relation to their exposure to WWTWs effluent. Sticklebacks were sampled in two successive years at fifteen sites in north-west England impacted by WWTW effluent and the response of each fish to the combined stressor of capture and a brief period of confinement was evaluated using both whole-body immunoreactive cortisol concentrations (WBIC) and the rate of release of cortisol to water (CRTW). A positive relationship between the magnitude of stress-induced CRTW in sticklebacks of both sexes and WWTW effluent concentration at site of capture was observed in both years. However, the relationship between stress-induced WBIC and WWTW effluent concentration was not consistent. These results suggest that components of WWTW effluent can modulate the magnitude of the neuroendocrine stress response in sticklebacks, and by inference in other fish species, but they raise questions about the measurement and interpretation of stress axis responses in fish via endpoints other than blood hormone concentrations. Possible factors underlying the disparity between the CRTW and WBIC results are discussed.

Disruption of the stress response in wastewater treatment works effluent-exposed three-spined sticklebacks persists after translocation to an unpolluted environment

The hypothalamic-pituitary-adrenal/interrenal (HPA/I) axis plays a key role in responding to biotic and abiotic challenges in all vertebrates. Recent studies have shown that the apical response of the HPI axis to stressors in three-spined sticklebacks varies in proportion to the concentration of wastewater treatment works (WWTW) effluent to which the fish are exposed. This study was conducted to determine whether between-site variation in stress responsiveness among WWTW effluent-exposed sticklebacks is persistent or reversible. Sticklebacks from eight sites in north-west England affected by WWTW effluent and exhibiting between-population variation in HPI axis reactivity, were moved to a clean-water aquarium environment. After five months in the contaminant-free environment the responsiveness of these fish to a standardised stressor was determined, by measuring the rate of stress-induced cortisol release across the gills, and compared with the responses of fish newly sampled from the eight original capture sites. Inter-site differences in the reactivity of the HPI axis, proportional to the effluent concentration at each site, persisted among the translocated female sticklebacks for at least 5 months. In male fish however, the direct relationship between stress responsiveness and site-specific effluent was not evident 5 months post-translocation. These results support previous observations that the HPA/I axis, a non-reproductive endocrine system, is vulnerable to modulation by anthropogenic factors in fish and show for the first time that, in female fish at least, this modulation is not transient. The mechanisms underlying these observations, and the implications for the fitness and resilience of affected populations, requires investigation.

Seasonal and sex differences in responsiveness to adrenocorticotropic hormone contribute to stress response plasticity in red-sided garter snakes (Thamnophis sirtalis parietalis)

Like many vertebrates, hormonal responses to stress vary seasonally in red-sided garter snakes (Thamnophis sirtalis parietalis). For example, males generally exhibit reduced glucocorticoid responses to a standard stressor during the spring mating season. We asked whether variation in adrenal sensitivity to adrenocorticotropic hormone (ACTH) explains why glucocorticoid responses to capture stress vary with sex, season, and body condition in red-sided garter snakes. We measured glucocorticoids at 0, 1, and 4 hours after injection with ACTH (0.1 IU/g body mass) or vehicle in males and females during the spring mating season and fall pre-hibernation period. Because elevated glucocorticoids can influence sex steroids, we also examined androgen and estradiol responses to ACTH. ACTH treatment increased glucocorticoids in both sexes and seasons. Spring-collected males had a smaller integrated glucocorticoid response to ACTH than fall-collected males. The integrated glucocorticoid response to ACTH differed with sex during the spring, with males having a smaller glucocorticoid response than females. Although integrated glucocorticoid responses to ACTH did not vary with body condition, we observed an interaction among season, sex and body condition. In males, ACTH treatment did not alter androgens in either season, but androgens decreased during the sampling period. Similar to previous studies, plasma estradiol was low or undetectable during the spring and fall and therefore any effect of ACTH treatment on estradiol could not be determined. These data provide support for a mechanism that partly explains how the HPA axis integrates information about season, sex, and body condition: namely, variation in adrenal responsiveness to ACTH.

Environmental chemicals active as human antiandrogens do not activate a stickleback androgen receptor but enhance a feminising effect of oestrogen in roach

Sexual disruption is reported in wild fish populations living in freshwaters receiving discharges of wastewater treatment works (WwTW) effluents and is associated primarily with the feminisation of males by exposure to oestrogenic chemicals. Antiandrogens could also contribute to the feminisation of male fish, but there are far less data supporting this hypothesis and almost nothing is known for the effects of oestrogens in combination with antiandrogens in fish. We conducted a series of in vivo exposures in two fish species to investigate the potency on reproductive-relevant endpoints of the antiandrogenic antimicrobials triclosan (TCS), chlorophene (CP) and dichlorophene (DCP) and the resin, abietic acid (AbA), all found widely in WwTW effluents. We also undertook exposures with a mixture of antiandrogens and a mixture of antiandrogens in combination with the oestrogen 17α-ethinyloestradiol (EE2). In stickleback (Gasterosteus aculeatus), DCP showed a tendency to reduce spiggin induction in females androgenised by dihydrotestosterone (DHT), but these findings were not conclusive. In roach (Rutilus rutilus), exposures to DCP (178 days), or a mixture of TCS, CP and AbA (185 days), or to the model antiandrogen flutamide (FL, 178 days) had no effect on gonadal sex ratio or on the development of the reproductive ducts. Exposure to EE2 (1.5ng/L, 185 days) induced feminisation of the ducts in 17% of the males and in the mixture of antiandrogens (TCS, CP, AbA) in combination with EE2, almost all (96%) of the males had a feminised reproductive ducts. In stickleback androgen receptor (ARα and ARβ) transactivation assays, the model antiandrogens, FL and procymidone inhibited 11-ketotestosterone (11-KT) induced receptor activation, but none of the human antiandrogens, TCS, CP, DCP and AbA had an effect. These data indicate that antimicrobial antiandrogens in combination can contribute to the feminisation process in exposed males, but they do not appear to act through the androgen receptor in fish.

Putting pharmaceuticals into the wider context of challenges to fish populations in rivers

The natural range of fish species in our rivers is related to flow, elevation, temperature, local habitat and connectivity. For over 2000 years, humans have altered to varying degrees the river habitat. In the past 200 years, we added to the environmental disruption by discharging poorly treated sewage, nutrients and industrial waste into our rivers. For many rivers, the low point arrived during the period of 1950s-1970s, when rapid economic development overrode environmental concerns and dissolved oxygen concentrations dropped to zero. In these more enlightened times, gross river pollution is a thing of the past in the Developed World. However, persistent legacy chemical contaminants can be found in fish long after their discharge ceased. Changes in habitat quality and morphology caused and continue to cause the disappearance of fish species. The range of fish stressors has now increased as temperatures rise, and non-native fish introductions bring new diseases. The threat from pharmaceuticals to fish populations remains hypothetical, and no studies have yet linked change in fish populations to exposure.

Measures of physiological stress: a transparent or opaque window into the status, management and conservation of species?

Conservation physiology proposes that measures of physiological stress (glucocorticoid levels) can be used to assess the status and future fate of natural populations. Increases in glucocorticoids may reflect a more challenging environment, suggesting that the influence of human activities on free-living animals could be quantified by measuring glucocorticoids. Biomedical studies suggest that chronic increases in glucocorticoids can have detrimental effects on survival and reproduction, which could influence the viability of populations. Here, we discuss the use of measurements of glucocorticoids in conservation physiology. We first provide an overview of the different methods to quantify glucocorticoids and their utility in conservation physiology. We then discuss five questions we think are essential for conservation physiologists to address. We highlight how intrinsic (e.g. sex, reproductive status, age, recent experiences) and ecological factors (e.g. predation, food availability, snowfall) can, by themselves or through their interactions with anthropogenic disturbances, affect the physiological stress response and mask any general patterns about the effects of anthropogenic disturbances on glucocorticoids. Using a meta-analysis, we show that anthropogenic disturbances are consistently associated with increased glucocorticoids regardless of the type of human disturbance. We also show that males may be more sensitive to anthropogenic disturbances than females and that faecal glucocorticoids, but not baseline plasma glucocorticoids, consistently increase in response to anthropogenic disturbances. Finally, we discuss how increases in glucocorticoids in free-living animals can sometimes enhance survival and reproduction. Unfortunately, our literature analysis indicates that this observation has not yet gained traction, and very few studies have shown that increases in glucocorticoid levels resulting from anthropogenic disturbances decrease survival or reproduction. We think that the use of measures of glucocorticoids in conservation physiology has tremendous potential, but there are still a number of methodological concerns, in addition to several crucial questions that should be addressed.

Populations of a cyprinid fish are self-sustaining despite widespread feminization of males

BACKGROUND

Treated effluents from wastewater treatment works can comprise a large proportion of the flow of rivers in the developed world. Exposure to these effluents, or the steroidal estrogens they contain, feminizes wild male fish and can reduce their reproductive fitness. Long-term experimental exposures have resulted in skewed sex ratios, reproductive failures in breeding colonies, and population collapse. This suggests that environmental estrogens could threaten the sustainability of wild fish populations.

RESULTS

Here we tested this hypothesis by examining population genetic structures and effective population sizes (N(e)) of wild roach (Rutilus rutilus L.) living in English rivers contaminated with estrogenic effluents. N(e) was estimated from DNA microsatellite genotypes using approximate Bayesian computation and sibling assignment methods. We found no significant negative correlation between N(e) and the predicted estrogen exposure at 28 sample sites. Furthermore, examination of the population genetic structure of roach in the region showed that some populations have been confined to stretches of river with a high proportion of estrogenic effluent for multiple generations and have survived, apparently without reliance on immigration of fish from less polluted sites.

CONCLUSIONS

These results demonstrate that roach populations living in some effluent-contaminated river stretches, where feminization is widespread, are self-sustaining. Although we found no evidence to suggest that exposure to estrogenic effluents is a significant driving factor in determining the size of roach breeding populations, a reduction in N(e) of up to 65% is still possible for the most contaminated sites because of the wide confidence intervals associated with the statistical model.

Anti-androgens act jointly in suppressing spiggin concentrations in androgen-primed female three-spined sticklebacks - prediction of combined effects by concentration addition

Increasing attention is being directed at the role played by anti-androgenic chemicals in endocrine disruption of wildlife within the aquatic environment. The co-occurrence of multiple contaminants with anti-androgenic activity highlights a need for the predictive assessment of combined effects, but information about anti-androgen mixture effects on wildlife is lacking. This study evaluated the suitability of the androgenised female stickleback screen (AFSS), in which inhibition of androgen-induced spiggin production provides a quantitative assessment of anti-androgenic activity, for predicting the effect of a four component mixture of anti-androgens. The anti-androgenic activity of four known anti-androgens (vinclozolin, fenitrothion, flutamide, linuron) was evaluated from individual concentration-response data and used to design a mixture containing each chemical at equipotent concentrations. Across a 100-fold concentration range, a concentration addition approach was used to predict the response of fish to the mixture. Two studies were conducted independently at each of two laboratories. By using a novel method to adjust for differences between nominal and measured concentrations, good agreement was obtained between the actual outcome of the mixture exposure and the predicted outcome. This demonstrated for the first time that androgen receptor antagonists act in concert in an additive fashion in fish and that existing mixture methodology is effective in predicting the outcome, based on concentration-response data for individual chemicals. The sensitivity range of the AFSS assay lies within the range of anti-androgenicity reported in rivers across many locations internationally. The approach taken in our study lays the foundations for understanding how androgen receptor antagonists work together in fish and is essential in informing risk assessment methods for complex anti-androgenic mixtures in the aquatic environment.

Acute exposure to offshore produced water has an effect on stress- and secondary stress responses in three-spined stickleback Gasterosteus aculeatus

Pollution is one of today's greatest problems, and the release of contaminants into the environment can cause adverse changes in vitally important biological pathways. In this study, we exposed three-spined stickleback Gasterosteus aculeatus to produced water (PW), i.e. wastewater from offshore petroleum production. PW contains substances such as alkylphenols (APs) and aromatic hydrocarbons (PAHs) known to induce toxicant stress and endocrine disruption in a variety of organisms. Following exposure to PW, a standardized confinement treatment was applied as a second stressor (PW-stress), testing how fish already under stress from the pollutant would respond to an additional stressor. The endpoint for analysis was a combination of blood levels of cortisol and glucose, in addition to transcribed levels of a set of genes related to toxicant stress, endocrine disruption and general stress. The findings of this study indicate that low doses of PW do not induce vitellogenin in immature female stickleback, but do cause an upregulation of cytochrome (CYP1A) and UDP-glucuronsyltransferase (UDP-GT), two biomarkers related to toxicant stress. However, when the second stressor was applied, both genes were downregulated, indicating that the confinement exposure had a suppressive effect on the expression of toxicant biomarkers (CYP1A and UDP-GT). Further, two of the stress related genes, heat shock protein 90 (HSP90) and stress-induced phosphoprotein (STIP), were upregulated in both PW- and PW-stress-treatment, but not in the water control confinement treatment, indicating that PW posed as a larger stress-factor than confinement for these genes. The confinement stressor caused an increased level of glucose in both control and PW-treated fish, indicating hyperglycemia, a commonly reported stress response in fish.